Single cell analysis reveals distinct immune landscapes in transplant and primary sarcomas that determine response or resistance to immunotherapy

Abstract

Immunotherapy fails to cure most cancer patients. Preclinical studies indicate that radiotherapy synergizes with immunotherapy, promoting radiation-induced antitumor immunity. Most preclinical immunotherapy studies utilize transplant tumor models, which overestimate patient responses. Here, we show that transplant sarcomas are cured by PD-1 blockade and radiotherapy, but identical treatment fails in autochthonous sarcomas, which demonstrate immunoediting, decreased neoantigen expression, and tumor-specific immune tolerance. We characterize tumor-infiltrating immune cells from transplant and primary tumors, revealing striking differences in their immune landscapes. Although radiotherapy remodels myeloid cells in both models, only transplant tumors are enriched for activated CD8+ T cells. The immune microenvironment of primary murine sarcomas resembles most human sarcomas, while transplant sarcomas resemble the most inflamed human sarcomas. These results identify distinct microenvironments in murine sarcomas that coevolve with the immune system and suggest that patients with a sarcoma immune phenotype similar to transplant tumors may benefit most from PD-1 blockade and radiotherapy.

The KrasG12D;Trp53fl/fl murine model of undifferentiated pleomorphic sarcoma is macrophage dense, lymphocyte poor, and resistant to immune checkpoint blockade

“…Consistent with other studies in this field [56,57], the TIME of transplanted KP tumours was more inflamed than spontaneous UPS, showing a 2-fold and 3-fold increase in CD4+ and CD8+ lymphocytes. These finding were also observed on a transcriptomic level as the Nano-String1 immunological profiling also demonstrated a trend towards higher T cell, adaptive immunity and NK pathways scores in the transplanted model, however these differences were not statistically significant.…”

“…Human UPS is a heterogenous sarcoma subtype and unsurprisingly, in this study, UPS was represented in all sarcoma immune classes. In the SIC A and B sarcomas, immune cells represented < 30% of the total cell fraction, with macrophages representing the dominant immune population [ 20 , 56 ]. The SIC A and B sarcomas were also associated with resistance to immune checkpoint inhibitors.…”

“…In our experiments, the number of total immune cells in both spontaneous and transplanted KP UPS models were low (<30%), and tumours were resistant to anti-PD1 and anti-CTLA4, thus we believe the KP UPS model characterized in this study is most aligned with a SIC A or B immunologically cold phenotype. In a recent study by Wisdom et al [ 56 ], they immunologically characterized a high mutation load mouse model of UPS (80-fold higher than the KP model) induced using a combination of Trp53 and carcinogen 3-methylcholanthrene (MCA) mutagenesis. In this model of UPS, both spontaneous and transplanted sarcomas were consistent with a SIC D or E (immune high) phenotype and were therapeutically sensitively to immune checkpoint blockade.…”

Assessing evolutionary and developmental transcriptome dynamics in homologous cell types

“…This will only become more relevant, as scRNA-seq studies continue to expand into investigating the impacts of different genetic backgrounds, or environmental variables. [59][60][61] Overall, we observe that our comparative gene coexpression module approach represents a valuable addition to discriminate distinct cell states, some of which can be shared amongst different cell types or even distinct developmental lineages. Especially among early, undifferentiated tissues, these module signatures can contain important temporal information across samples, but also-for more mature cell types-signals relevant for comparisons between distantly related species, mutant backgrounds, and environmental parameters.…”

Assessing evolutionary and developmental transcriptome dynamics in homologous cell types

“…This will only become more relevant, as scRNA-seq studies continue to expand into investigating the impacts of different genetic backgrounds, or environmental variables. 63–65…”